MG11 
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Abstract

Phase space reduction through horizon constraints

Requiring the presence of a horizon imposes constraints on the physical phase space. After a careful analysis of dilaton gravity in 2D with boundaries (including the Schwarzschild and Witten black holes as prominent examples), it is shown that the classical physical phase space is smaller as compared to the generic case if horizon constraints are imposed. Conversely, the number of gauge symmetries is larger for the horizon scenario. In agreement with a recent conjecture by 't Hooft, we thus find that physical degrees of freedom are converted into gauge degrees of freedom at a horizon.

A target space action for the exact string black hole

The exact string black hole discovered by Dijkgraaf, Verlinde and Verlinde in 1992 emerges from a simple local target space action, a particular Poisson-sigma model. Its construction is reviewed, following hep-th/0501208, and some features are discussed, in particular concerning mass and T-duality.